Closed-loop (CL) multiple-input-multiple-output (MIMO) is a technique for enhancing the performance of a link (also referred to as a channel) between a transmitting antenna (such as an antenna located at a base station) and a receiving antenna (such as an antenna located at a mobile station) by providing the transmitter with knowledge about the channel state. The transmitter may have full or partial information about a matrix of channel coefficients, and the transmitter can use that information to increase the capacity and improve the performance of the link. Closed-loop MIMO operation will be a feature of the IEEE 802.16 wireless broadband standard (popularly known as Worldwide Interoperability for Microwave Access, or WiMAX), and specifically of 802.16e Rev2 (also known as Ver1.5) and of 802.16m. Closed loop MIMO is a generalization of beamforming for the case of more than one transmitted stream (i.e., an output from a MIMO encoder). In certain embodiments, beamforming includes the use of signal processing techniques such as “precoding” matrices that weight the various transmitted signal streams in order to improve system performance.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments of the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements, while similar reference numerals may, but do not necessarily, denote similar elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Similarly, if a method is described herein as comprising a series of steps, the order of such steps as presented herein is not necessarily the only order in which such steps may be performed, and certain of the stated steps may possibly be omitted and/or certain other steps not described herein may possibly be added to the method. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. Objects described herein as being “adjacent to” each other may be in physical contact with each other, in close proximity to each other, or in the same general region or area as each other, as appropriate for the context in which the phrase is used. Occurrences of the phrase “in one embodiment” herein do not necessarily all refer to the same embodiment.